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;------------------------------------------------------------------------------
;
; Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
; SPDX-License-Identifier: BSD-2-Clause-Patent
;
; Module Name:
;
; DisablePaging64.Asm
;
; Abstract:
;
; AsmDisablePaging64 function
;
; Notes:
;
;------------------------------------------------------------------------------
DEFAULT REL
SECTION .text
;------------------------------------------------------------------------------
; VOID
; EFIAPI
; InternalX86DisablePaging64 (
; IN UINT16 Cs,
; IN UINT32 EntryPoint,
; IN UINT32 Context1, OPTIONAL
; IN UINT32 Context2, OPTIONAL
; IN UINT32 NewStack
; );
;------------------------------------------------------------------------------
global ASM_PFX(InternalX86DisablePaging64)
ASM_PFX(InternalX86DisablePaging64):
cli
lea rsi, [.0] ; rsi <- The start address of transition code
mov edi, [rsp + 0x28] ; rdi <- New stack
lea rax, [mTransitionEnd] ; rax <- end of transition code
sub rax, rsi ; rax <- The size of transition piece code
add rax, 4 ; Round RAX up to the next 4 byte boundary
and al, 0xfc
sub rdi, rax ; rdi <- Use stack to hold transition code
mov r10d, edi ; r10 <- The start address of transicition code below 4G
push rcx ; save rcx to stack
mov rcx, rax ; rcx <- The size of transition piece code
rep movsb ; copy transition code to top of new stack which must be below 4GB
pop rcx ; restore rcx
mov esi, r8d
mov edi, r9d
mov eax, r10d ; eax <- start of the transition code on the stack
sub eax, 4 ; eax <- One slot below transition code on the stack
push rcx ; push Cs to stack
push r10 ; push address of tansition code on stack
DB 0x48 ; prefix to composite "retq" with next "retf"
retf ; Use far return to load CS register from stack
; Start of transition code
.0:
mov esp, eax ; set up new stack
mov rax, cr0
btr eax, 31 ; Clear CR0.PG
mov cr0, rax ; disable paging and caches
mov ebx, edx ; save EntryPoint to rbx, for rdmsr will overwrite rdx
mov ecx, 0xc0000080
rdmsr
and ah, ~ 1 ; clear LME
wrmsr
mov rax, cr4
and al, ~ (1 << 5) ; clear PAE
mov cr4, rax
push rdi ; push Context2
push rsi ; push Context1
call rbx ; transfer control to EntryPoint
hlt ; no one should get here
mTransitionEnd:
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